How to set up aliases

Aliases allow you to have different email addresses which all deliver to your one FastMail account, without needing to buy multiple accounts. This can help you to sort email. For example, you might have a sales@mydomain.com address for sales inquiries, and a press@mydomain.com address for news inquiries.

Aliases cannot be used as your username when you log in; you must always use the full account username.

How to create an alias

You'll see a table with any current aliases you have. The last row of this table is blank to allow you to add a new alias. Simply fill in the username you want and pick a domain from the list, then click the "Add" button.

Aliases can be used to direct email to other accounts, even non-FastMail ones. See the "Alias target" section below for a detailed description of how the Target field works.

The SRS column should be left unchecked unless required; please see the description below to find out if you need this.

How to disable an alias

You can disable an alias by unticking the box in the Active column for that alias, then clicking "Save Changes" in the top or bottom left. Any further email sent to that alias will now bounce (be returned to the sender as undeliverable).

How to remove an alias

To remove an alias, click the "Del" link in the far right of the row. This will cause any email sent to the alias to bounce, but will allow another user to create that alias in the future, unless you own the domain of the alias.

Alias target

Email sent to an alias will be forwarded on to the email address (or addresses) specified in the Target column. By default, the target of all aliases is your account. You can, however, change the target of an alias to be any other account, including other FastMail accounts or a completely external email address.

You can target multiple accounts by putting a comma (,) separated list of email addresses. If you do that, a copy of each email will be delivered to each target address. This can be a useful way to direct a copy of all email to a separate backup account at another provider if you want. To do that, create an account and set up an alias that targets both your account and the external account you want backups to go to. Then, when you tell people about your email address, tell them your alias address, never your account's address.

You can also change targets to use plus addressing. Commonly, you might want email sent to a particular alias to go into a certain folder. The easiest way to do this is to use plus addressing with the "Target". If you have a folder "aliasmessages", set the target to be youraddress+aliasmessages@fastmail.com and any email sent to the alias will automatically be put in the "aliasmessages" folder. One thing to note is that alias targeting occurs before spam scanning or any rules are applied to a message.

External targets and SRS rewriting

On the aliases screen, there is an SRS checkbox for each alias. This can be useful if you have an external target (non-FastMail email address) for one of your aliases, and the target server you're forwarding to uses SPF to block emails.

SPF is a way for domain owners to authorise only particular servers to send email with a particular SMTP MAIL FROM envelope. The problem is that when email is forwarded by a service, the SMTP MAIL FROM envelope should be preserved. When that happens, it looks like the forwarding service is trying to send email with the same SMTP MAIL FROM envelope as the original service, which is blocked because the forwarding service hasn't been authorised. This is a bug with the design of SPF. There is a (fairly ugly) way to work around this though, and it's called SRS rewriting.

You can enable SRS rewriting for email sent to a particular alias just by enabling the SRS checkbox on that alias. We don't recommend enabling SRS unless you need to (i.e. emails aren't being forwarded correctly).

To get an idea of what SRS is, and what it does, here's an example. Say I have an alias abc@fastmail.com that targets xyz@gmail.com:

Someone sends an email from their Yahoo account def@yahoo.com to abc@fastmail.com. So the email has an SMTP MAIL FROM envelope of def@yahoo.com and an SMTP RCPT envelope of abc@fastmail.com.

We accept the email, and see it's an alias with target xyz@gmail.com. We forward the email with the SMTP RCPT TO envelope of xyz@gmail.com, and by default preserve the SMTP MAIL FROM envelope of def@yahoo.com.

However at this point, Gmail looks at the SMTP MAIL FROM envelope, sees @yahoo.com, does an SPF check and says "hold on, 66.111.4.25 (one of FastMail's outgoing IPs) hasn't been authorised by SPF to send email with an SMTP MAIL FROM envelope of @yahoo.com". It therefore rejects the message: SPF has broken forwarding.

When you activate SRS, we change the following.

We accept the email, and see it's an alias with target xyz@gmail.com. We forward the email with the SMTP RCPT TO envelope of xyz@gmail.com, and we alter the SMTP MAIL FROM envelope of def@yahoo.com to use SRS rewriting which creates something like SRS0+abcd=Cw=yahoo.com=def@srs.messagingengine.com. Since @srs.messagingengine.com is a domain we control, so there's no SPF issue.

If for some reason the email ends up bouncing, the NDN will be sent back to SRS0+abcd=Cw=yahoo.com=def@srs.messagingengine.com, which we'll get, then unwrap and send back to def@yahoo.com.